1. Field of the Invention
This invention relates to electrophotographic image-forming members sensitive to electromagnetic waves such as light (herein used in a wide sense, representing ultraviolet rays, visible light, infrared rays, X-rays, .gamma.-rays, etc.) and used in the image-forming technique area.
2. Description of the Prior Art
Referring to photoconductive materials constructing photoconductive layers in electrophotographic image-forming members, there are well known Se, Se-Te CdS, ZnO, and organic photoconductive materials such as PVCz, TNF, and the like. Meanwhile, amorphous silicon (hereinafter, denoted by a-Si) has become of major interest lately as a photoconductive material promising in that, as described in, e.g. German Patent Offen Nos. 2746967 and 2855718. It has characteristics comparable to other photoconductive materials in photosensitivity, spectral wave length region, light-response, and dark resistance, and in addition, its p-n control is easy in spite of the amorphous form, and it is harmless to the human body.
Because of such character of a-Si superior to that of other photoconductive materials in many respect, its practical application to electrophotographic image-forming members has been rapidly pushed forward, but it is still leaving problems to be solved.
For example, image-forming members employing a-Si will cause objectionable phenomena, such as remainder of residual potential during use, fatigue accumulation during long-term repeated operations, and ensuing ghost phenomenon and whitening in transfer images.
Moreover, when the thickness of a-Si layer exceeds more than ten microns, the layer becomes, with the lapse of time of standing in the air after removal from a vacuum deposition, liable to cause such phenomena as peeling or separating from the supporting substrate and crack development therein. These phenomena tend to occur frequently in particular when its supporting substrate is of a drum shape, which is usually employed in the field of electrophotography. Thus, there are problems to be solved in aging stability.
In view of the above, this invention has been accomplished after studying the results of many intensive studies on the following matters: that is, the present inventors formed photoconductive layers from amorphous materials comprising silicon as matrix and at least either one of hydrogen atoms (H) and halogen atoms (X) [hereinafter, these amorphous materials denoted by a-Si (H, X)] and investigated the characteristics of said layers and the relation between said layers and the substrates supporting them, from the standpoints of mechanical, electrical, and photoconductive properties and of durability.
According to studies by the present inventors, a-Si (H, X) seems to have a large strain when forming a layer, therefore the layer may peel off or separate from the supporting substrate or crack in itself. It is hence necessary to obtain the following objectives: to remove the strain of the formed layer or relax it to such an extent that it has no adverse effect, by some means; to optimize the mechanical and electrical contact between the substrate and the a-Si (H, X) layer; to improve the adhesion between them; and to establish such optimum conditions as to satisfy at the same time the above-mentioned needs, in order to obtain an electrophotographic image-forming member excellent in electrophotographic characteristics, particularly in durability. Thereafter, as a result of a great deal of studies and investigations, they were successful in establishment of the optimum conditions.